Most cyclonic separation devices take the form of a cylindrical vessel with a tapered conical section which tapers to one of the product outlets or alternatively, a tapered conical section without a cylindrical section. The materials to be separated are introduced at the wide end of the cone or, if a cylindrical section is present, at the opposite end of the cylinder to the conical section. The method of introduction for the materials to be separated is such as to cause the materials to rotate about the axis of the vessel as they progress through the vessel. This rotation is typically instigated using one or more tangential inputs for the feed mixture or by feeding the feed mixture axially through a set of shaped blades or by other suitable means. As the materials to be separated move away from the feed, the rotary motion of the flow moves the heavier or higher density components towards the perimeter of the vessel and the lighter and/or finer components towards the core. As the materials move into the conical area, the lighter and/or finer components begin to reverse flow in an ongoing spiral back towards the inlet end where in general they are able to exit through a central aperture. This aperture is often fitted with a short tubular connection which projects for a short distance into the vessel. This is often referred to as a vortex finder. The portion of the feed mixture which leaves via this exit at the feed end is often referred to as the overhead product.
The remainder of the feed mixture, containing the heavier or higher density components that have migrated towards the perimeter of the vessel, moves towards the narrow end of the conical section, progressively displacing most of the lighter and/or finer components and a proportion of the carrier fluid from within itself as it does so. As a result of this progressive displacement, the heavier portion becomes more concentrated. This heavier portion then leaves via a connection at the end of the conical section. This portion of the feed mixture if often referred to as the underflow.
The cyclonic separation device that was presented in PCT/ZA2003/000160 has all the product outputs at the opposite end to the feed end. This not only lends itself to simple “within the pipe line” styles of installations, it also enables closely packed arrangements to be created within carrier vessels.
These structural differences also affect the flow profiles within the unit. In a normal cyclone with its overhead product leaving at the feed end, the flow profiles consists of an outer vortex flow from the inlet towards the underflow exit with an inner vortex flow in the opposite direction. Also, because both exit flows leave via smaller (usually much smaller) radius conduits relative to the radius of the outer vortex, there is a considerable radial velocity component within the unit. The principle of conservation of momentum causes the circumpherential velocity to increase as the fluids move radially inwards. Overall, therefore, there are considerable variations in velocity between immediately neighbouring elements of the fluid within a normal type of cyclone vessel. These variations result in local shear and eddies which in turn affect the particle separation efficiency. Also, in the case of applications involving froth or dispersed air types of floatation, the froth and the particle-gas combinations are subject to considerable levels of destruction.
Where the product streams leave at the opposite end to the feed end, and where both products leave via large diameter connections, the internal radial velocity components can be arranged to be relatively low and the reverse flowing central vortex can be avoided. Alternatively, should it be appropriate, relatively modest radial velocities accompanied by a reasonably low intensity reverse flow central vortex can also be set up. For example, in the case of liquid based systems, the intensity of this radial component and the reverse flow vortex can be adjusted on line by simply adjusting the size of the gas core. A large diameter gas core will yield very little radial velocity and reverse flow vortex and as the diameter of the gas core is reduced so the magnitude of them can be increased.
These flow profiles and their adjustability within liquid based systems can be very advantageous in the context of liquid-liquid separations and in the context of Froth or Dispersed Air Floatation applications. These flow profiles and their adjustability will have a less pronounced benefit but none the less a significant benefit on the separation efficiency of suspended solids. The importance and benefit of controlling the diameter of the gas core within a normal style of hydrocyclone device is clearly shown within PCT WO 02/076622. In this disclosure, an additional gas core controlling conical aperture is concentrically inserted into the top of the normal overflow outlet connection and it is used to control the diameter of the core and the intensity of the shear (and hence eddy mixing) which occurs adjacent to the core. The technology that is presented herein enables the diameter of the gas core to be controlled in an on-line adjustable manner within this somewhat different style of cyclonic separator and to achieve this control not just with a single unit but when a closely packed group of such units are arranged within a carrier vessel. The technology presented within PCT WO 02/076622 relies on a fixed size of orifice. Obviously the orifice can be replaced with a different size of orifice but on-line adjustment is not available.
It must be remembered that the type of cyclonic separation device that is presented in this disclosure is not in general able to create such a thick and well dewatered underflow stream as can be achieved with a typical hydrocyclone unit.
The need to control the stability of the gas core is also referred to within WO 03089148. This disclosure also presents the concept whereby an additional, concentric and extended central vortex finder reaches down to at least the top of the conical section within a normally shaped hydrocyclone and/or cyclone. This additional vortex finder is able to remove a selected portion of what would otherwise be mostly included in the overhead product. In the main, this selected portion of the overhead product is that which is displaced from the most concentrated part of the underflow product as it concentrates itself in the lower portion of the cone. In general therefore, relative to the rest of the overhead product, this portion contains a much higher proportion of mid and oversize components. In addition, for a normal hydrocyclone or cyclone, this portion of the central vortex is created at a position which is at or very close to the centre line. This means that the centrifugal forces which act upon it as it rises up the centre of the core are generally not strong enough to clear all of the mid and oversize components out of it before it reaches the overhead outlet. By separately collecting and recycling this relatively small proportion of the total flow the authors claim a very much improved quality of separation within the remainder of the product streams.
Typically within a normal hydrocyclone, the gas core can source its supply of gas from either the overhead connection or the underflow connection as well as via the feed. In some instances, depending upon the style of connection which is fitted to the overhead and underflow outlets, gas can be drawn through the unit from the underflow to the overhead product. In these circumstances the quality of the overhead product can be affected not only by the gas inclusion but also by the poorer separation of the larger solids from the liquor which is routed to the overhead product from the last thickening stages of the underflow product.
GB897057 presents a device which can be mounted within the vortex finder for the overhead product and which prevents the gas core from being removed with the overhead product, unless that core exceeds a particular size.
This same type of concept is reported in U.S. Pat. No. 48,438,434 but in this instance it is used to prevent the gas core from being removed within the underflow. It is also used within a froth floatation application inside a cyclone to create a “support pillar” for the separated froth so that the froth is forced to exit as part of the overhead product. This same disclosure also presents a range of differently shaped support pillars which by inference are very instructive as to the manner with which material moves from the main outer vortex into the inner reverse direction vortex within a normal hydrocyclone.
The concepts which are presented herein avoid the reverse direction central vortex, the relatively high radial velocities, the dewatering function of the underflow close to the centre line and the small diameter gas core. Instead, the coarse solids are not forced towards the centre line by the shape of the cyclone body, and there is the option to use a connection at either the feed end or the outlet end through which the diameter of the gas core can be controlled.
CA 1178383 presents one of the earliest disclosures for the concept of carrying out gas injection through the walls of a cyclonic separator so as to create a froth floatation or dispersed air floatation style of device within the enhanced gravitational field of a cyclone. Here the non-floated material is removed via an annularly connected tangential outlet and the froth is removed using a counter flowing vortex through a central vortex tinder type of connection at the slurry inlet end. A permeable wall for the hydrocyclone is mounted within an outer container and is used to supply the compressed air for the floatation process. The equipment had a tangential inlet for the slurry feed and in general sought to keep a relatively thin slurry layer on the inside wall of the generally cylindrical and permeable wall within the equipment. In this way they were able to limit the magnitude of the shear between the upward flowing central vortex of froth and the downward outer vortex of aerated slurry.
U.S. Pat. No. 4,997,549 introduces wash water sprays to clean the froth before the froth leaves via the overhead product. In most other respects the equipment that is described in U.S. Pat. No. 4,997,549 has a lot of similarities to that which is disclosed in CA 1178382.
WO 9119572 uses a similar concept to that presented in CA 1178382 except that an orifice plate type of obstruction is fitted at the bottom of the permeable wall part of the cyclonic body. Beneath this orifice plate type of obstruction the underflow fraction was able to degas itself so as to create a reasonably gas free product. The underflow product from the CA 1178382 style of equipment contained a significant proportion of gas bubbles.
The equipment which is presented herein is arranged to be able to degas the underflow product without the need for such on orifice type of obstruction and without all the blockage issues that accompany such an obstruction. These blockage issues would be particularly acute if the feed slurry contained heavy components (such as metal fragments), or inadequately screened oversize materials.
One way of avoiding the issues associated with pore blockage within a permeable wall unit is to separately supply a layer of froth beneath an incoming and already spinning layer of feed slurry. This concept is disclosed in U.S. Pat. No. 4,971,685. The principle draw back of this equipment is the limited ability of the separately created froth to maintain its function throughout the equipment. This equipment used an annular collection arrangement for the underflow product and a disc type of froth support pillar.
Another disclosure where the froth is pre-made before it enters the separation device is presented in CA 2246841. This disclosure relates to the recovery of bitumous oil from the large deposits of bitumous oil sands which are found in western Canada. Careful slurry preparation and extensive pre-conditioning and air addition upstream of the cyclonic device is needed in order to separate the bulk of the bitumous oil off the surfaces of the sand particles before the slurry enters the separator.
The separator has multiple (usually two) tangential inlets at one end, an annular collection zone with tangential off-takes for the residual sand slurry at the other end and a central froth outlet for the bitumous float, also at the opposite end to the feed. At the top of the off-take for the bitumous float there is an annular platform which is designed to act as a froth support platform. This platform enables the froth to separate itself into a reasonably sand free float fraction which then passes on down through the hole in the middle of the annular platform. The annular platform also enables the sand slurry to be able to reasonably de-aerate itself before it passes around the outside of the annular platform. The equipment has a reasonably low pressure drop relative to the claimed particle size of sand which is kept out of the float fraction. However, it is anticipated that the degree of removal of the bituminous oil is not as high as it otherwise could be if                a) good particle on particle scraping were achieved and/or        b) wash water or additional froth were provided towards the end of the separation process to sweep the residual fine bitumen particles out of the mother liquor which is incorporated with the sand fraction.        
The later parts of the disclosures that are made herein seek in particular to address these two technical features.